How hard is it to tag starfish? The modern technique is to implant a microchip, like a veterinarian implants under a pet’s skin. In fact, the procedure for implanting chips in starfish wasn’t all that difficult for Frederik Ekholm, Gaardsted Christensen, and Trine Bottos Olsen of the University of Southern Denmark. But keeping them tagged turned out to be a problem.

Starfish came to the university from local fishers who had caught them by accident. The students injected the tags into the animals as directed. But within days, those same tags showed up at the bottom of the tank. Somehow, the starfish were expelling the foreign objects from their bodies.

When the students witnessed the act, it was a little like a magic trick—one moment a magician’s hand is empty, and the next she’s holding a bird. The starfish pushed the tags out the ends of their arms, straight through the skin.

To find out more, the students and professor Daniel Levitis set up some experiments. First they injected tags into 53 starfish and scanned them each day to see how many of the tags were still there. In less than 3 weeks, all the tags were gone.

Well, this is what science is like. Your original research idea hits a snag, and now you have something completely different to investigate. They used magnets. They used ultrasound. And they found out that starfish have a magical power to get rid of foreign objects in their bodies. Read about the research at Discover magazine. The conclusion: starfish are weird. -via Metafilter